Federal and local authorities this week ramped up the search for Joseph Jakubowski, who they believe stole at least 16 handguns and two assault rifles from the Armageddon Gun Shop in Janesville after mailing his 161-page anti-government manifesto to D.C.

His writings, which also included anti-religion sentiments, were addressed to President Trump.

The 32-year-old suspect’s stepfather, Donald McLean, told WKOW Jakubowski could be looking to end his life in a showdown with law enforcement.

Joseph Jakubowski is suspected of stealing firearms from a gun store in Janesville, threatening an unspecified attack that prompted several schools to close and sending an anti-government manifesto to President Trump.

(AP)

""That's what I'm afraid of the most. That he ain't going to back down," he added.

Nine years ago, a Janesville police officer threatened to shoot Jakubowski after he attempted to wrestle a gun away from another officer. "Just (expletive) do it," he said, according to a criminal complaint against him.

McLean said the incident contributed to his stepson's distaste for authority, a trait coupled with an appreciation for firearms.

The criminal complaint unveiled Tuesday also showed that Jakubowski's sister found that her brother wrote an apology letter to the gun shop owner, thanking him for supporting the 2nd Amendment.

The exterior of Armageddon Gun Shop in Janesville.

(Angela Major/AP)

Jakubowski allegedly explained in the note that he wanted the weapons to protect his family, but could not buy them because he is a felon.

Authorities have described Jakubowski as “highly agitated” by the current political climate and an associate revealed to investigators the suspect had previously spoken about a plan to carry out some type of attack.

“The most dangerous people in this genre are the ones whose ideology is kind of all over the place and they don’t really fit in with the neo-Nazis, the skin heads,” Chris Swecker, a former head of the FBI criminal investigation division, told NBC News. “They’re off on their own.”

Swecker added: “He seems like kind of a ticking time bomb.”

FBI agents provide tactical support to sheriff's detectives during a search for Joseph Jakubowski, in Janesville, Wis.

(Angela Major/AP)

Authorities confirmed Jakubowski’s manifesto reached the White House last week and recently released a video that appears to show him mailing the package.

“To anybody that got this letter you might want to read it,” Jakubowski says in the video as he walks toward a post office, stamped envelope in hand. “There it is, you see, it’s getting shipped. Revolution. It’s time for change.”

Authorities said it's clear Jakubowski has a plan, though they're still not sure "what his end game is."

“He’s trying to make a statement,” McLean told the news station. “Ten years from now no one’s going to know his name.”

The FBI is on Tuesday doubled their reward offer for any information leading to Jakubowski's arrest to $20,000.